1. Field of Invention
The present invention relates to a semiconductor process. More particularly, the present invention relates to a method of forming a composite opening and a dual damascene process using the same.
2. Description of Related Art
With the progress of integration of semiconductor devices, the use of multi-metal interconnects are becoming wide spread. Usually, the lower the resistance of the metal layer of the multi-metal interconnects is, the higher the reliability of elements is, and the better the performance of the element can be. Among metal materials, the copper is suitable to be used for the multi-metal interconnects because the resistance of copper is low. However, as it is difficult to pattern the copper in the conventional photolithographic etching technique, a dual damascene process has been developed.
The dual damascene process is a technique that involves forming a trench and a via opening in a dielectric layer and then refilling a metal to form a metal wire and a via. The dual damascene process includes many methods which involve forming a via opening in the dielectric layer first and then forming a trench; and forming the trench first and then forming the via.
When the method of forming the via opening first and then forming the trench is employed in the dual damascene process, in the etching process of forming the trench, the corresponding metal layer under the via opening may be damaged by etching, thus causing the electrical problem of elements.
Referring to FIG. 1, in order to prevent the corresponding metal layer 102 under the via opening from being damaged by etchant in the etching process of forming the trench, a recent method includes after a via opening 110 is formed in a dielectric layer 106, first filling a gap fill material 112 in the via opening 110 to prevent the corresponding metal layer 102 under the via opening 110 from being damaged by etchant. However, in the method, usually because of the shadowing effect of the gap fill material 112, after the trench 120 is formed in the subsequent etching, a dielectric layer 106a with a fence shape is left at a corner 110a of the via opening 110, thus causing the problem of the reliability of elements. However, it is quite difficult to eliminate the fence-shaped dielectric layer. It is applicable to adjust the height of the gap fill material to prevent the forming of the fence-shaped dielectric layer. However, under the influence of uniformity of etching and micro-loading effect, the thicknesses of the gap fill material at the center of the substrate and at the edge of the substrate, or the thicknesses of the gap fill material in a dense region and in a loose region of the substrate are greatly different, such that the process window is very narrow.
In another aspect, referring to FIG. 2, in order to prevent the forming of the fence-shaped dielectric layer in the etching process, a polymer light process is adopted in a trench etching process. But, without the protection of the polymer, the dielectric layer 106 at the corner 120a of the trench 120 is easily damaged by the etchant, and thus the corner 120a of the trench 120 is rounded. After the metal layer 122 is deposited subsequently to fill in the trench with the rounded corner, the two neighboring dual damascene structures may be bridged subsequently.